<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %> 
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>随机验证码生成页面</title>
	<meta http-equiv="pragma" content="no-cache"/>
	<meta http-equiv="cache-control" content="no-cache"/>
	<meta http-equiv="expires" content="0"/>
  </head>
  <img border=0 src="image.jsp"> <!--  只需要把该代码发在验证码要显示的区域就可以了） -->
	<%! 
		public static String code="abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; 
		//给定范围获得随机颜色 
		Color getRandColor(int fc,int bc){
			Random random = new Random(); 
			if(fc>255) {
				fc=255;
			}
			if(bc>255) {
				bc=255;
			}
			int r=fc+random.nextInt(bc-fc); 
			int g=fc+random.nextInt(bc-fc); 
			int b=fc+random.nextInt(bc-fc); 
			return new Color(r,g,b); 
		} 
	%> 
	<% 
		//设置页面不缓存 
		response.setHeader("Pragma","No-cache"); 
		response.setHeader("Cache-Control","no-cache"); 
		response.setDateHeader("Expires", 0); 
		// 在内存中创建图象,设置图片的显示大小 
		int width=60, height=20; 
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); 
		// 获取图形上下文 
		Graphics g = image.getGraphics(); 
		// 生成随机类 
		Random random = new Random(); 
		// 设定背景色 
		g.setColor(getRandColor(200,250)); 
		g.fillRect(0, 0, width, height); 
		//设定字体 
		g.setFont(new Font("Times New Roman",Font.PLAIN,18)); 
		//画边框 
		//g.setColor(new Color()); 
		//g.drawRect(0,0,width-1,height-1); 
		// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到 
		g.setColor(getRandColor(160,200)); 
		for (int i=0;i<155;i++) 
		{ 
			int x = random.nextInt(width); 
			int y = random.nextInt(height); 
			int xl = random.nextInt(12); 
			int yl = random.nextInt(12); 
			g.drawLine(x,y,x+xl,y+yl); 
		} 
		// 取随机产生的认证码(由数字和字母组长的) 
		String sRand=""; 
		for (int i=0;i<4;i++){ 
			int rand=random.nextInt(62); 
			sRand+=String.valueOf(code.charAt(rand)); 
			// 将认证码显示到图象中 
			g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
			// 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成 
			g.drawString(String.valueOf(code.charAt(rand)),13*i+6,16); 
		} 
		// 将认证码存入SESSION 
		session.setAttribute("rand",sRand); 
		// 图象生效 
		g.dispose(); 
		// 输出图象到页面 
		ImageIO.write(image, "JPEG", response.getOutputStream()); 
	%> 
</html>
